pacu mum, i'm surprised that you would think adding more volume (a sump) would be inefective, i would have thought that is the whole point buy a bigger tank, more surface area and volume, higher nitrate dilution..........wrong?? For instance if i was to have a spare 4' tank lying around (which it so happens i do) then what ever the volume of my sump set up is would directly corolate to the amount my water be diluted of nitrate,Yes???